Substrate pretreatment for subsequent high temperature group iii depositions

ABSTRACT

Embodiments of the present invention relate to apparatus and method for pretreatment of substrates for manufacturing devices such as light emitting diodes (LEDs) or laser diodes (LDs). One embodiment of the present invention comprises pre-treating the aluminum oxide containing substrate by exposing a surface of the aluminum oxide containing substrate to a pretreatment gas mixture, wherein the pretreatment gas mixture comprises ammonia (NH 3 ) and a halogen gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No.61/172,606 (Attorney Docket No. 14308L), filed Apr. 24, 2009, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to the manufacture ofdevices such as light emitting diodes (LEDs) or laser diodes (LDs). Moreparticularly, embodiments of the present invention relate to apparatusand method for pretreatment of substrates for manufacturing devices suchas light emitting diodes (LEDs) or laser diodes (LDs).

2. Description of the Related Art

Group III nitride semiconductors are finding greater importance in thedevelopment and fabrication of a variety of semiconductor devices, suchas short wavelength light emitting diodes (LEDs), laser diodes (LDs),and electronic devices including high power, high frequency, hightemperature transistors and integrated circuits. Light emitting diodes(LEDs) and laser diodes (LDs) are fabricated by depositing group-IIInitrides on sapphire substrates. Group-III nitrides can be deposited byhydride vapor phase epitaxy (HYPE), metal organic chemical vapordeposition (MOCVD), chemical vapor deposition (CVD), and/or physicalvapor deposition (PVD) on aluminum oxide containing substrates, such assapphire substrates.

Aluminum oxide containing substrates need to be pretreated beforedeposition of group-III nitrides to generate low defect densitygroup-III nitride layers. However, traditional methods for treatingaluminum oxide containing substrates may leave by-products on walls ofreaction chamber, exhaust lines, and pumps contaminating themanufacturing processes and reducing yield of the facility.

Therefore, there is a general need for methods and apparatus fortreating aluminum oxide containing substrates with reduced by-productformation.

SUMMARY OF THE INVENTION

The present invention generally provides apparatus and methods formanufacturing devices such as light emitting diodes (LEDs) or laserdiodes (LDs). Particularly, embodiments of the present invention relateto apparatus and methods for pretreatment of substrates formanufacturing devices such as light emitting diodes (LEDs) or laserdiodes (LDs).

One embodiment of the present invention provides a method for forming agroup-III metal nitride film, comprising heating one or more aluminumoxide containing substrates to a pretreatment temperature, and exposinga surface of each of the one or more aluminum oxide containingsubstrates to a pretreatment gas mixture when the surface is at thepretreatment temperature to form a pretreated surface, wherein thepretreatment gas mixture comprises ammonia (NH₃) and a halogen gas. Insome embodiments, the halogen gas comprises chlorine (Cl₂) gas.

Another embodiment of the present invention provides a method forforming a group-III metal nitride film, comprising heating one or morealuminum oxide containing substrates to a pretreatment temperature,exposing a surface of each of the one or more aluminum oxide containingsubstrates to a pretreatment gas mixture when the surface is at thepretreatment temperature to form a pretreated surface, wherein thepretreatment gas mixture comprises ammonia (NH₃), a metal halide gas andan etchant containing gas that comprises a halogen gas, and forming ametal nitride layer over the pretreated surface.

Another embodiment of the present invention provides a method forforming a compound nitride structure, comprising providing a substratehaving an aluminum oxide containing surface, forming a buffer film onthe aluminum oxide containing surface by etching the aluminum oxidecontaining surface to form AlON or AlN using a gas mixture comprisingammonia and chlorine, and forming a gallium nitride film from aprecursor gas mixture comprising a gallium source and a nitrogen source.

Yet another embodiment of the present invention provides a method forforming compound nitride structures comprising providing a plurality ofsapphire substrates, positioning the plurality of sapphire substrates ina processing chamber, flowing a first gas mixture to the processingchamber while heating the plurality of sapphire substrates, flowing apretreatment gas mixture to the processing chamber, wherein thepretreatment gas mixture comprises ammonia and a halogen gas, andflowing a precursor gas mixture to form a group-III metal nitride filmon the plurality of sapphire substrates, wherein the precursor gasmixture comprises a group-III metal source and a nitrogen source.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a schematic sectional side view of a GaN based LED structure.

FIG. 1B is a schematic sectional side view of a GaN based LD structure.

FIG. 2 is a flow diagram of a method for pretreating a substrateaccording to one embodiment of the present invention.

FIG. 3 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 4 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 5 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 6 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 7 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 8 is a flow diagram of a method according to one embodiment of thepresent invention.

FIG. 9 is a cluster tool according to one embodiment of the presentinvention.

FIG. 10 is a schematic sectional view of an HVPE chamber in accordancewith one embodiment of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments of the present invention relate to the manufacture ofdevices such as light emitting diodes (LEDs) or laser diodes (LDs). Moreparticularly, embodiments of the present invention relate to apparatusand method for pretreatment of aluminum oxide containing substrates formanufacturing devices such as light emitting diodes (LEDs) or laserdiodes (LDs).

One embodiment of the present invention provides treating a substratehaving an aluminum oxide containing surface by exposing the aluminumoxide containing surface to a pretreatment gas mixture comprisingammonia and an etchant containing gas, wherein the etchant containinggas comprises a halogen gas. The halogen gas may be selected from thegroup consisting of fluorine gas, chlorine gas, bromine gas, iodine gas,combinations thereof, and mixtures thereof. The gas mixture of ammoniaand halogen etches the aluminum oxide containing substrates and forms alayer, or a formed region, of aluminum nitride (AlN) and/or aluminumoxynitride (AlON) on the aluminum oxide containing substrate. The layerof AlON or AlN can work as a buffer layer for subsequent group-III metalnitride depositions. Buffer layers can be used to minimize the number ofcrystalline defects created by the lattice mismatch between thesubstrate material and the deposited film layer(s), and also reduce, ortune, the film stress in the subsequently deposited layers.Pre-treatment to aluminum oxide containing substrates using ammonia andhalogen gas can be used for preparation of any deposition techniques,such as HVPE, MOCVD, CVD, and PVD.

Embodiments of the present invention have advantages over traditionalpre-treatment and nitridation of aluminum oxide containing substratesbecause the use of a halogen gas in the pretreatment process produces adrastic decrease in the formation of harmful by-products. For example,ammonia chloride (NH₄Cl) forms as a by-product in traditionalpre-treatment of sapphire substrates using HCl and ammonia beforedepositing group-III nitride layers on the sapphire substrates. Ammoniachloride may sublime to a solid powder and stick to walls of thereaction chamber, exhaust line and vacuum pump. The ammonia chloridepowder may also be transmitted through the entire processing system, forexample with the substrates, carriers, or robots. By drastic decrease inthe formation of harmful by-product, embodiments of the presentinvention improves throughput and increases quality in applicablemanufacturing processes, such as manufacturing of LEDs and LDs.

In one embodiment, a nitriding process is performed in combination withexposing the aluminum oxide containing substrate to the pretreatment gasmixture. The nitriding processes may be performed by exposing thealuminum oxide containing substrates with a nitriding gas mixturecomprising a nitrogen source. The nitrogen source may be ammonia. Thenitriding process may be performed prior to or after the pretreatmentprocess.

In one embodiment, a group-III metal nitride buffer layer is formedafter pretreatment. The group-III metal nitride buffer layer may analuminum nitride buffer layer or gallium nitride buffer layer. Thealuminum nitride buffer layer may be formed on the aluminum oxidecontaining substrate by exposing the substrate to a buffering gasmixture comprising an aluminum precursor. The gallium nitride bufferlayer may be formed on the aluminum oxide containing substrate byexposing the substrate to a buffering gas mixture comprising a galliumprecursor and a nitrogen source. In another embodiment, the group-IIImetal nitride buffer layer is formed simultaneously with thepretreatment by simultaneously flowing a nitrogen source, such asammonia, a halogen gas, such as chlorine gas, and a group-III metalhalide precursor, such as aluminum chloride or gallium chloride. In oneembodiment, the pretreatment process further comprises a nitridingprocess and a buffer layer forming process. The buffer layer maycomprise an aluminum nitride (AlN) and/or aluminum oxynitride (AlON), orgallium nitride (GaN).

FIG. 1A is a schematic sectional side view of a gallium nitride basedLED structure 100. The LED structure 100 is fabricated over an aluminumoxide containing substrate 104. The substrate 104 may be formed fromsolid aluminum oxide, such as single crystal sapphire substrate having aC-axis crystal orientation of (0001). The substrate 104 may also be acomposite substrate having a surface containing aluminum oxide forfabricating a compound nitride structure thereon. Any well known method,such as masking and etching may be utilized to form features from aplanar substrate to create a patterned substrate. In a specificembodiment, the patterned substrate is a (0001) patterned sapphiresubstrate (PSS). Patterned sapphire substrates may be ideal for use inthe manufacturing of LEDs because they increase the light extractionefficiency which is useful in the fabrication of a new generation ofsolid state lighting devices.

In one embodiment, the LED structure 100 is formed on the substrate 104after a pretreatment process. The thermal cleaning procedure may beperformed by exposing the substrate 104 to a cleaning gas mixturecomprising ammonia and carrier gas while the substrate 104 is beingheated. In one embodiment, the pretreatment process comprises exposingthe substrate to a pretreatment gas mixture while the substrate isheated an elevated temperature range. In one embodiment, thepretreatment gas mixture is an etching agent comprising a halogen gas.In one embodiment, the pretreatment gas mixture comprises a halogen gasand ammonia. As shown in FIG. 1A, the LED structure 100 formed on thesubstrate 104 generally comprises a buffer layer 112 deposited over thecleaned and pretreated substrate 104. The buffer layer 112 may be formedby a HVPE process or a MOCVD process. Traditionally, the buffer layer112 may be deposited by providing Gallium and Nitrogen precursors andheat to a processing chamber to achieve deposition. A typical bufferlayer 112 has a thickness of about 300 Å, which may be deposited at atemperature of about 550° C. for about five minutes. In one embodimentof the present invention, the buffer layer 112 is an aluminum nitride(AlN) layer formed after or during the pretreatment process to thesubstrate 104.

An n-GaN (n-doped GaN) layer 116 is subsequently deposited on the GaNbuffer layer 112. The n-GaN layer 116 may be formed by a HVPE process ora MOCVD process. In one embodiment, n-GaN layer 116 may be deposited ata higher temperature, for example at about 1050° C. The n-GaN layer 116is relatively thick, with deposition of a thickness on the order of 4 μmrequiring about 140 minutes.

An InGaN multi-quantum-well (MQW) layer 120 is subsequently depositedover the n-GaN layer 116. The InGaN MQW layer 120 may have a thicknessof about 750 Å and take about about 40 minutes to form at about 750° C.

A p-AlGaN (p-doped AlGaN) layer 124 is deposited over themulti-quantum-well layer 120. The p-AlGaN layer 124 may have a thicknessof about 200 Å and take about five minutes at a temperature of about950° C. to form.

A p-GaN (p-doped GaN) contact layer 128 is then deposited over thep-AlGaN layer 124. The p-GaN contact layer 128 may have a thickness ofabout 0.4 μm requiring about 25 minutes to form at about 1050° C.

FIG. 1B is a schematic sectional side view of a GaN based LD structure150 formed on an aluminum oxide containing substrate 105. The aluminumoxide containing substrate 105 may be similar to the aluminum oxidecontaining substrate 104 of FIG. 1A. The substrate 105 may be formedfrom solid aluminum oxide, such as sapphire (0001). The substrate 105may also be a composite substrate having a surface containing aluminumoxide for fabricating a compound nitride structure thereon.

In one embodiment, the LD structure 150 is formed on the substrate 105after a thermal cleaning procedure and a pretreatment process. Thethermal cleaning procedure may be performed by exposing the substrate105 to a cleaning gas mixture comprising ammonia and carrier gas whilethe substrate 105 is being heated. In one embodiment, the pretreatmentprocess comprises exposing the substrate to a pretreatment gas mixturewhile the substrate is heated to an elevated temperature. In oneembodiment, the pretreatment gas mixture is an etching agent comprisinga halogen gas.

The LD structure 150 is a stack of group-III metal nitride layers formedon the substrate 105. The LD structure 150 starts from an n-type GaNcontact layer 152. The LD structure 150 further comprises an n-typecladding layer 154. The cladding layer 154 may comprise AlGaN. Anundopped guide layer 156 is formed over the cladding layer 154. Theguide layer 156 may comprise InGaN. An active layer 158 having amultiquantum well (MQW) structure is formed on the guide layer 156. Aundoped guide layer 160 is formed over the active layer 158. A p-typeelectron block layer 162 is formed over the undoped guide layer 160. Ap-type contact GaN layer 164 is formed over the p-type electron blocklayer 162.

FIG. 2 is a flow diagram of a method 200 for treating a substrateaccording to one embodiment of the present invention.

In box 210, one or more aluminum oxide containing substrates are loadedin a processing chamber. In one embodiment, the aluminum oxidecontaining substrates may be sapphire substrates. In one embodiment, aplurality of sapphire substrates may be positioned in a substratecarrier and transferred into the processing chamber. The substratecarrier is generally adapted to support the substrates duringprocessing. The substrate carrier 616 (FIG. 10) may include one or morerecesses within which one or more substrates may be disposed duringprocessing. The substrate carrier may carry six or more substrates. Inone embodiment, the substrate carrier carries eight substrates. It is tobe understood that more or fewer substrates may be carried on thesubstrate carrier. Substrate size may range from 50 mm-100 mm indiameter or larger, while substrate carrier size may range from 200mm-500 mm in diameter. The substrate carrier 616 may be formed from avariety of materials, including SiC or SiC-coated graphite.

In one embodiment, the processing chamber may be designated for cleaningand treating the substrates for subsequent deposition. The cleaned andtreated substrates are then transferred to one or more depositionchambers to deposit the layers used to form the LED or LD structures. Inanother embodiment, the one or more aluminum oxide containing substratesmay be loaded in a process chamber wherein at least one layer of filmsof the LED or LD structure is subsequently formed.

In box 220, the one or more aluminum oxide containing substrates may beheated in the process chamber while a carrier gas is delivered into theprocessing volume of a process chamber. The carrier gas may comprisenitrogen gas, an inert gas such as argon or helium, or combinationsthereof. In one embodiment, a thermal cleaning may be performed to theone or more aluminum oxide containing substrates while heating thesubstrates. In one embodiment, the thermal cleaning may be performed byflowing a cleaning gas mixture into the processing chamber while heatingthe one or more substrates to a cleaning temperature. In one embodiment,the cleaning gas mixture comprises ammonia and carrier gas. In oneembodiment, the carrier gas comprises nitrogen gas (N₂). The cleaningtemperature may be between about 900° C. and about 1100° C. In oneexample, the cleaning temperature may be between about 900° C. and about1050° C. In another example, the cleaning temperature may be greaterthan about 900° C. In one example, the thermal cleaning process may beperformed by flowing the cleaning gas mixture for about 10 minutes whilemaintaining the substrate(s) at a temperature of about 1050° C. Thethermal cleaning procedure may take additional time, such as on theorder of 10 minutes, so that the temperature can be ramped-up andramped-down. In one embodiment, the temperature ramp-up rate is about 1°C./second to about 5° C./second, or other ramp rate depending on thehardware of the process chamber. In one embodiment, the cleaning gas maybe delivered into the process chamber during the temperature ramp-up andramp-down times.

In box 230, the one or more substrates are exposed to a pretreatment gasmixture at an elevated temperature for a pretreatment to enable highquality GaN film to be formed over the aluminum oxide containingsubstrates. In one embodiment, the pretreatment process may be performedat a temperature range between about 500° C. to about 1200° C. In oneembodiment, the pretreatment process may be performed at a temperaturerange between about 600° C. to about 1150° C. In one embodiment, thepretreatment process may be performed at a temperature between about 900and about 1000° C. In one example, the pretreatment process temperaturemay be greater than about 900° C.

The pretreatment gas mixture may comprise ammonia and a halogen gasselected from the group consisting of fluorine gas (F₂), chlorine gas(Cl₂), bromine gas (Br₂), iodine gas (I₂), combinations thereof, andmixtures thereof.

In one embodiment, the pretreatment gas mixture comprises ammonia andchlorine gas and the pretreatment comprises converting the aluminumoxide containing substrates to AlON or AlN by etching the aluminum oxidecontaining substrates in the presence of the ammonia and chlorine. Inone embodiment, exposing the one or more aluminum oxide containingsubstrates to the pretreatment gas mixture comprises flowing ammonia gasat a flow rate between about 500 sccm to about 9000 sccm and flowingchlorine gas at a flow rate between about 200 sccm to about 1000 sccm.In one embodiment, the pretreatment may be performed for about 1 minuteto about 20 minutes.

In box 240, a group-III metal nitride film is formed over a treatedsurface of the aluminum oxide containing substrate. The group-III metalnitride film may be formed by a HVPE process, a MOCVD process, a CVDprocess, or a PVD process. In one embodiment, the group-III metalnitride film may be deposited by providing flows of a group-III metaland nitrogen precursors to a processing chamber and using thermalprocesses to achieve deposition. In one example, the group-III metalprecursor may be a metal halide precursor gas, which is discussed below.In one embodiment, the group-III metal nitride film is formed in thesame chamber where pretreatment is performed. In another embodiment, thegroup-III metal nitride film may be formed in a separate process chamberfrom the process chamber where thermal cleaning and pretreatment areperformed.

In one embodiment, a GaN film may be formed during the process of box240 by a HVPE process. In one embodiment, the HVPE process comprisesflowing a gallium containing precursor and a nitrogen source over theone or more substrates at a temperature between about 550° C. to about1100° C. In one embodiment, the pretreatment process temperatureperformed at box 230 is less than the HVPE process temperature, such as100° C. less. In one embodiment, the HVPE process comprises flowing agallium chloride containing precursor and a nitrogen source over the oneor more substrates at a temperature between about 950° C. to about 1100°C. In one embodiment, the gallium containing precursor may be generatedby flowing chlorine gas at a flow rate between about 20 sccm to about150 sccm over liquid gallium maintained at a temperature between 50° C.to about 1000° C. During the deposition processes, the chamber pressuremay be maintained between about 10 Torr and about 760 Torr, such asbetween about 70 Torr and about 550 Torr, for example about 450 Torr,and the chamber wall temperature is maintained at or above about 450° C.The nitrogen source may be ammonia at a flow rate between about 1 SLM toabout 20 SLM. In another embodiment, the nitrogen source may be one ormore active nitrogen species derived from a remote plasma of anitrogen-containing material such as nitrogen gas (N₂), nitrous oxide(N₂O), ammonia (NH₃), hydrazine (N₂H₄), diimide (N₂H₂), hydrazoic acid(HN₃), and the like. While the term hydride vapor phase epitaxy (HVPE)is used to describe a type of deposition process described herein,typically the processes described herein use a halogen gas (e.g., Cl₂)in place of a hydride containing deposition gas (e.g., HCl) during thedeposition process, and thus this term is not intended to limiting as tothe scope of the invention described herein.

FIG. 10 is a schematic sectional view of an HVPE apparatus 600 which canbe used to deposit a metal nitride film, such as the GaN film formedusing the processes described in box 240. The HVPE apparatus 600includes a chamber 602 enclosed by a lid 604. The chamber 602 and thelid 604 define a processing volume 607. A showerhead 606 is disposed inan upper region of the processing volume 607. A susceptor 614 isdisposed opposing the showerhead 606 in the processing volume 607. Thesusceptor 614 is configured to support a plurality of substrates 615thereon during processing. In one embodiment, the plurality ofsubstrates 615 are disposed on a substrate carrier 616 which issupported by the susceptor 614. The susceptor 614 may be rotated by amotor 680, and may be formed from a variety of materials, including SiCor SiC-coated graphite.

In one embodiment, the HVPE apparatus 600 comprises a heating assembly628 configured to heat the substrates 615 on the susceptor 614. In oneembodiment, chamber bottom 602 a is formed from quartz and the heatingassembly 628 is a lamp assembly disposed under the chamber bottom 602 ato heat the substrates 615 through the quartz chamber bottom 602 a. Inone embodiment, the heating assembly 628 comprises an array of lampsthat are distributed to provide a uniform temperature distributionacross the substrates, substrate carrier, and/or susceptor.

The HVPE apparatus 600 further comprises precursor supplying pipes 622,624 disposed inside the side wall 608 of the chamber 602. The pipes 622and 624 are in fluid communication with the processing volume 607 and aninlet tube 621 found in a precursor source module 632. The showerhead606 is in fluid communication with the processing volume 607 and a firstgas source 610. The processing volume 607 is in fluid communication withan exhaust 651 through an outlet 626.

The HVPE apparatus 600 further comprises a heater 630 embedded withinthe walls 608 of the chamber 602. The heater 630 embedded in the walls608 may provide additional heat if needed during the deposition process.A thermocouple may be used to measure the temperature inside theprocessing chamber. Output from the thermocouple may be fed back to acontroller 641 that controls the temperature of the walls of the chamber602 by adjusting the power delivered to the heater 630 (e.g., resistiveheating elements) based upon the reading from a thermocouple (notshown). For example, if the chamber is too cool, the heater 630 will beturned on. If the chamber is too hot, the heater 630 will be turned off.Additionally, the amount of heat provided from the heater 630 may becontrolled so that the amount of heat provided from the heater 630 isminimized.

Processing gas from the first gas source 610 is delivered to theprocessing volume 607 through the gas distribution showerhead 606. Inone embodiment, the first gas source 610 may comprise a nitrogencontaining compound. In one embodiment, the first gas source 610 isconfigured to deliver a gas that comprises ammonia or nitrogen. In oneembodiment, an inert gas such as helium or diatomic nitrogen may beintroduced as well either through the gas distribution showerhead 606 orthrough the pipe 624, disposed on the walls 608 of the chamber 602. Anenergy source 612 may be disposed between the first gas source 610 andthe gas distribution showerhead 606. In one embodiment, the energysource 612 may comprise a heater or a remote RF plasma source. Theenergy source 612 may provide energy to the gas delivered from the firstgas source 610, so that radicals or ions can be formed, so that thenitrogen in the nitrogen containing gas is more reactive.

The source module 632 comprises a halogen gas source 618 connected to awell 634A of a source boat 634 and an inert gas source 619 connected tothe well 634A. A source material 623, such as aluminum, gallium orindium, is disposed in the well 634A. A heating source 620 surrounds thesource boat 634. An inlet tub 621 connects the well 634A to theprocessing volume 607 via the pipes 622, 624.

In one embodiment, during processing a halogen gas (e.g., Cl₂, Br₂, F₂,or I₂) is delivered from the halogen gas source 618 to the well 634A ofthe source boat 634 to create a metal halide gas, or metal halideprecursor gas. In one embodiment, the metal halide gas is a group-IIImetal halide gas, such as gallium chloride (e.g., GaCl, GaCl₃), indiumchloride (e.g., ICl₃) or aluminum chloride (e.g., AlCl₃). Theinteraction of the halogen gas and the solid or liquid source material623 allows a metal halide precursor to be formed. The source boat 634may be heated by the heating source 620 to heat the source material 623and allow the metal halide precursor to be formed. The metal halideprecursor is then delivered to the processing volume 607 of the HVPEapparatus 600 through an inlet tube 621. In one embodiment, an inert gas(e.g., Ar, He, N₂) delivered from the inert gas source 619 is used tocarry, or push, the metal halide precursor formed in the well 634Athrough the inlet tube 621 and pipes 622 and 624 to the processingvolume 607 of the HVPE apparatus 600. A nitrogen-containing precursorgas (e.g., ammonia (NH₃), N₂) may be introduced into the processingvolume 607 through the showerhead 606, while the metal halide precursoris also provided to the processing volume 607, so that a metal nitridelayer can be formed on the surface of the substrates 615 disposed in theprocessing volume 607.

FIG. 3 is a flow diagram of a method 300 according to one embodiment ofthe present invention. Method 300 comprises performing a nitridationprocess prior to the pretreatment to one or more aluminum oxidecontaining substrates.

In box 310, one or more aluminum oxide containing substrates are loadedin a processing chamber. In one example, the processing chamber issimilar to the HVPE apparatus 600, described above. In one embodiment,the aluminum oxide containing substrates are sapphire substrates.

In box 320, the one or more aluminum oxide containing substrates areheated or thermally cleaned in a process similar to the processdescribed above with box 220 of the method 200.

In box 325, a nitridation process is performed on the one or morealuminum oxide containing substrates. During nitridation, the one ormore aluminum oxide containing substrates may be heated to a temperaturebetween about 850° C. to about 1100° C. while flowing a nitriding gasmixture to the process chamber for about 5 minutes to about 15 minutes.In one embodiment, the nitriding gas mixture comprises ammonia and acarrier gas. In one embodiment, the carrier gas is nitrogen gas. In oneembodiment, the total flow rate of the nitriding gas mixture is betweenabout 3 SLM to about 16 SLM.

In box 330, the substrates are exposed to a pretreatment gas mixture atan elevated temperature to enable a high quality GaN film to be formedover the aluminum oxide containing substrate after the nitridingprocess. In one embodiment, the pretreatment process comprisesconverting the aluminum oxide containing substrates to AlON or AlN byetching the aluminum oxide containing substrates in the presence of theammonia and chlorine. The process in box 330 is similar to the processdescribed above with box 230 of the method 200.

In box 340, a group-III metal nitride film is forming over the treatedsurface of the aluminum oxide containing substrates. The processesperformed in box 340 may be similar to the processes described above inconjunction with box 240 of the method 200.

FIG. 4 is a flow diagram of a method 300a according to one embodiment ofthe present invention. The method 300a is similar to the method 300except that a nitriding process is performed after a pretreatment.

In box 310, one or more aluminum oxide containing substrates are loadedin a processing chamber. In one example, the processing chamber issimilar to the HVPE apparatus 600, described above. In one embodiment,the aluminum oxide containing substrates are sapphire substrates.

In box 320, similar to the process performed in box 220 of method 200,the one or more aluminum oxide containing substrates may be heated or athermal cleaning may be performed to the one or more aluminum oxidecontaining substrates during heating.

In box 330 a, similar to the pretreatment performed in box 230 of method200, the one or more substrates are exposed to a pretreatment gasmixture at an elevated temperature to enable high quality GaN film to beformed over the aluminum oxide containing substrates. Just like in box330 and box 230, a layer of AlON or AlN is formed on the aluminum oxidecontaining substrates by etching the aluminum oxide containingsubstrates in the presence of the ammonia and chlorine.

In box 335, after pretreatment, a nitridation process is performed overthe one or more aluminum oxide containing substrates. The nitridationprocess in box 335 is similar to the nitridation process of 325 ofmethod 300. During nitridation, the one or more aluminum oxidecontaining substrates may be heated to a temperature between about 850°C. to about 1100° C. while flowing a nitriding gas mixture to theprocess chamber for a bout 5 minutes to about 15 minutes.

In box 340, a group-III metal nitride film is formed over the treatedsurface of the aluminum oxide containing substrate, similar to thegroup-III metal nitride film forming process of box 240 of method 200.

FIG. 5 is a process flow diagram illustrating a method 400 according toone embodiment of the present invention. The method 400 disclosestreatments to one or more aluminum oxide containing substrates prior toforming a GaN film for a LED or LD structure. The method 400 comprisesthermal cleaning, nitriding, and forming a buffer layer on the one ormore aluminum oxide containing substrates prior to forming a group-IIImetal nitride film for a LED or LD structure.

In box 410, one or more aluminum oxide containing substrates are loadedin a processing chamber. In one example, the processing chamber issimilar to the HVPE apparatus 600 described above.

In box 420, the one or more aluminum oxide containing substrates areheated and/or cleaned using processes similar to the thermal cleaningprocess described in box 220 of method 200.

In box 425, a nitriding process is then performed on the one or morealuminum oxide containing substrates by exposing the one or morealuminum oxide containing substrates to a nitriding gas mixture whileheating the substrate. The nitriding process may be similar to thenitriding process described in box 325 of method 300.

In box 436, a buffer layer is then formed on the one or more aluminumoxide containing substrates. The buffer layer may comprise aluminumnitride (AlN) and/or aluminum oxynitride (AlON), or gallium nitride(GaN).

In one embodiment, the buffer layer comprises AlN formed by HVPE usingammonia as a nitrogen source, and an aluminum halide gas generated byflowing a halogen over an aluminum metal source. For example, the bufferlayer may be formed using the HVPE apparatus 600 shown in FIG. 6. Thebuffer layer may be formed by generating a metal halide precursor, suchas an aluminum chloride precursor, and flowing the metal halideprecursor and a nitrogen-containing precursor gas to the processingregion 607 in the process chamber 602 while maintaining the one or moresubstrates at a temperature between about 550° C. to about 950° C. Inone embodiment, the aluminum chloride precursor is generated by flowingchlorine gas (Cl₂) over solid aluminum at a flow rate between about 70sccm to about 140 sccm with the solid aluminum maintained at atemperature between about 50° C. to about 650° C. In one embodiment, thealuminum source material is maintained between about 450° C. to about650° C. In one embodiment, the aluminum source material is disposed in alocation remote of the substrate processing region, the processingtemperature of the aluminum source may be maintained between about 50°C. to about 150° C.

In one embodiment, the buffer layer may be formed by flowing a galliumchloride precursor and a nitrogen source to the process chamber whileheating the one or more substrates to a temperature between about 550°C. to about 1100° C. The cleaning temperature may be between about 900and about 1100° C. In one embodiment, the buffer layer may be formed byflowing a gallium chloride precursor and a nitrogen source to theprocess chamber while heating the one or more substrates to atemperature between about 950 and about 1100° C. In one example, thetemperature is maintained at about 1050° C. In one embodiment, thegallium chloride precursor is generated by flowing chlorine gas overgallium at a flow rate between about 5 sccm to about 300 sccm withgallium maintained at a temperature between about 550° C. to about 1000°C. In one embodiment, the gallium chloride precursor is generated byflowing hydrogen chloride gas over gallium at a flow rate between about5 sccm to about 300 sccm with gallium maintained at a temperaturebetween about 550° C. to about 1000° C.

In one embodiment, the nitrogen source may be ammonia. In anotherembodiment, the nitrogen source may be one or more active nitrogenspecies derived from a remote plasma of a nitrogen-containing materialsuch as nitrogen gas (N₂), nitrous oxide (N₂O), ammonia (NH₃), hydrazine(N₂H₄), diimide (N₂H₂), hydrazoic acid (HN₃), and the like. In oneembodiment, the flow rate of nitrogen source may be between about 3000sccm to about 9000 sccm.

In box 440, a group-III metal nitride film is formed over treatedsurface of the aluminum oxide containing substrate, similar to thegroup-III metal nitride film forming process of box 240 of method 200.

FIG. 6 is a process flow diagram illustrating a method 500 according toone embodiment of the present invention. The method 500 disclosestreatments to one or more aluminum oxide containing substrates prior toforming a GaN film for a LED or LD structure. The method 500 comprisesthermal cleaning, nitriding, pretreating, and forming a buffer layer onthe one or more aluminum oxide containing substrates prior to forming agroup-III metal nitride film for a LED or LD structure.

In box 510, the one or more aluminum oxide containing substrates arepositioned in a processing chamber. In one example, the processingchamber is similar to the HVPE apparatus 600 described above.

In box 520, the one or more aluminum oxide containing substrates areheated and/or cleaned using processes similar to the thermal cleaningprocess described in box 220 of method 200.

In box 525, a nitriding process is then performed on the one or morealuminum oxide containing substrates by exposing the one or morealuminum containing substrate to a nitriding gas mixture while heatingthe substrate. The nitriding process may be similar to the nitridingprocess described in box 325 of method 300.

In box 530, the one or more substrates are exposed to a pretreatment gasmixture at an elevated temperature for a pretreatment to enable highquality GaN film to be formed over the aluminum oxide containingsubstrate. Just like in box 330 and box 230, a layer of AlON or AlN isformed on the aluminum oxide containing substrates by etching thealuminum oxide containing substrates in the presence of the ammonia andchlorine.

In box 536, a buffer layer is then formed on the pre-treated aluminumoxide containing substrates. The buffer layer may comprise aluminumnitride (AlN) and/or aluminum oxynitride (AlON), or gallium nitride. Inone embodiment, the buffer layer is formed by one of the processesdescribed above with box 436 of the method 400.

In box 540, a group-III metal nitride film is formed over the treatedsurface of the aluminum oxide containing substrate, similar to thegroup-III metal nitride film forming process of box 240 of method 200.

FIG. 7 is a process flow diagram illustrating a method 700 according toone embodiment of the present invention. The method 700 is similar tothe method 500 of FIG. 6 except a nitridation process is performed afterthe pretreatment process.

In box 710, the one or more aluminum oxide containing substrates arepositioned in a processing chamber. In one example, the processingchamber is similar to the HVPE apparatus 600 described above.

In box 720, the one or more aluminum oxide containing substrates areheated and/or cleaned using processes similar to the thermal cleaningprocess described in box 220 of method 200.

In box 730, the one or more substrates are exposed to a pretreatment gasmixture at an elevated temperature for a pretreatment to enable highquality GaN film to be formed over the aluminum oxide containingsubstrate, similar to the pretreatment process described in box 530 ofmethod 500.

In box 735, a nitriding process is then performed on the one or morealuminum oxide containing substrates by exposing the one or morealuminum oxide containing substrate to a nitriding gas mixture whileheating the substrate. The nitriding process may be similar to thenitriding process described in box 325 of method 300.

In box 736, a buffer layer is then formed on the one or more aluminumoxide containing substrates. The buffer layer may comprise aluminumnitride (AlN) and/or aluminum oxynitride (AlON), or gallium nitride. Thebuffer layer may be formed in a similar way as described in box 536 ofmethod 500.

In box 740, a group-III metal nitride film is formed over the treatedsurface of the aluminum oxide containing substrate, similar to thegroup-III metal nitride film forming process of box 240 of method 200.

FIG. 8 is a flow diagram of a method 800 according to one embodiment ofthe present invention. The method 800 discloses treatments to one ormore aluminum oxide containing substrates prior to forming a GaN filmfor a LED or LD structure. The method 800 comprises a combined processof pretreating and forming a buffer layer on the one or more aluminumoxide containing substrates prior to forming a group-III metal nitridefilm for a LED or LD structure.

In box 810, one or more aluminum oxide containing substrates are loadedin a processing chamber. In one example, the process is performed in achamber similar to the HVPE apparatus 600 discussed above.

In box 820, the one or more aluminum oxide containing substrates goesthrough a heating or a thermal cleaning process similar to the thermalcleaning process described in box 220 of method 200.

In box 830, the one or more substrates are exposed to apretreatment/buffer gas mixture for a pretreatment to the aluminum oxidecontaining surface and forming a buffer layer. In one embodiment, thepretreatment/buffer gas mixture comprises a nitrogen source, a halogengas, and an aluminum or gallium containing precursor. The nitrogensource may be ammonia. The halogen gas may be selected from the groupconsisting of fluorine gas, chlorine gas, bromine gas, iodine gas,combinations thereof, and mixtures thereof. The aluminum containingprecursor may be aluminum chloride precursor generated from flowingchlorine gas over solid aluminum maintained at high temperature, similarto the aluminum precursor described in description of box 536.

In box 840, a group-III metal nitride film is forming over treatedsurface of the aluminum oxide containing substrate, similar to thegroup-III metal nitride film forming process of box 240 of method 200.

As discussed above, the methods described according to embodiments ofthe present invention may be performed in a single chamber, or performedin two or more changes in a cluster tool.

In one embodiment, when processes of a method are performed in a singlechamber, ammonia and/or nitrogen gas may be flown constantly during theprocess during temperature ramp-up, temperature ramp-down, thermalcleaning, pretreatment, nitridation, buffer layer deposition, and GaNdeposition.

In another embodiment, one or more substrates may be treated in achamber first, then move to a different chamber within a tool forsubsequent processing. FIG. 9 is a cluster tool 900 may be used in aprocess according to one embodiment of the present invention. Thecluster tool 900 is configured to form nitride compound structures forLED and/or LD.

In one embodiment, the cluster tool 900 comprises one HVPE chamber 902and multiple MOCVD chambers 903 a and 903 b connected to a transferchamber 906 for fabricating compound nitride semiconductor devicesaccording to embodiments described herein. Although one HVPE chamber 902and two MOCVD chambers 903 a and 903 b are shown, it should beunderstood that any combination of one or more MOCVD chambers with oneor more HVPE chambers may also be coupled with the transfer chamber 906.For example, in one embodiment, the cluster tool 900 may comprise 3MOCVD chambers. In another embodiment, the processes described hereinmay be performed in a single MOCVD chamber. It should also be understoodthat although a cluster tool is shown, the embodiments described hereinmay also be performed using a linear processing system.

In one embodiment, an additional chamber 904 is coupled with thetransfer chamber 906. The additional chamber 904 may be an MOCVDchamber, an HVPE chamber, a metrology chamber, a degassing chamber, anorientation chamber, a cool down chamber, a pretreatment/precleanchamber, a post-anneal chamber, or the like. In one embodiment, thetransfer chamber 906 is six-sided and hexagonal in shape with sixpositions for process chamber mounting. In another embodiment, thetransfer chamber 906 may have other shapes and have five, seven, eight,or more sides with a corresponding number of process chamber mountingpositions.

The HVPE chamber 902 is adapted to perform HVPE processes in whichgaseous metal halides are used to epitaxially grow thick layers ofcompound nitride semiconductor materials on heated substrates. The HVPEchamber 902 comprises a chamber body 914 where a substrate is placed toundergo processing, a chemical delivery module 918 from which gasprecursors are delivered to the chamber body 914, and an electricalmodule 922 that includes the electrical system for the HVPE chamber ofthe cluster tool 900. In one embodiment, the HVPE chamber 902 may besimilar to the HVPE apparatus 600 described in FIG. 10.

Each MOCVD chamber 903 a, 903 b comprises a chamber body 912 a, 912 bforming a processing region where a substrate is placed to undergoprocessing, a chemical delivery module 916 a, 916 b from which gasessuch as precursors, purge gases, and cleaning gases are delivered to thechamber body 912 a, 912 b and an electrical module 920 a, 920 b for eachMOCVD chamber 903 a, 903 b that includes the electrical system for eachMOCVD chamber of the cluster tool 900. Each MOCVD chamber 903 a, 903 bis adapted to perform CVD processes in which metalorganic precursors(e.g., TMG, TMA) react with metal hydride elements to form thin layersof compound nitride semiconductor materials.

The cluster tool 900 further comprises a robot assembly 907 housed inthe transfer chamber 906, a load lock chamber 908 coupled with thetransfer chamber 906, a batch load lock chamber 909, for storingsubstrates, coupled with the transfer chamber 706. The cluster tool 900further comprises a load station 910, for loading substrates, coupledwith the load lock chamber 908. The robot assembly 907 is operable topick up and transfer substrates between the load lock chamber 908, thebatch load lock chamber 909, the HVPE chamber 902, and the MOCVDchambers 903 a, 903 b. In one embodiment, the load station 910 is anautomatic loading station configured to load substrates from cassettesto substrate carriers or to the load lock chamber 908 directly, and tounload the substrates from substrate carriers or from the load lockchamber 908 to cassettes.

The transfer chamber 906 may remain under vacuum and/or at a pressurebelow atmosphere during the process. The vacuum level of the transferchamber 906 may be adjusted to match the vacuum level of correspondingprocessing chambers. In one embodiment, the transfer chamber 906maintains an environment having greater than 90% N₂ for substratetransfer. In another embodiment, the transfer chamber 906 maintains anenvironment of high purity NH₃ for substrate transfer. In oneembodiment, the substrate is transferred in an environment havinggreater than 90% NH₃. In another embodiment, the transfer chamber 906maintains an environment of high purity H₂ for substrate transfer. Inone embodiment, the substrate is transferred in an environment havinggreater than 90% H₂.

The cluster tool 900 further comprises a system controller 960 whichcontrols activities and operating parameters. The system controller 960includes a computer processor and a computer-readable memory coupled tothe processor. The processor executes system control software, such as acomputer program stored in memory.

In one embodiment, one of the processing chamber 902, 903 a, 903 b, or904 is configured to clean and pretreat the substrates according tomethods described above prior to forming LED/LD structures. In oneembodiment, the substrates may be cleaned, pretreated, nitriding, and/orcovered with a buffer layer in the HVPE chamber 902, then moved toprocessing chambers 903 a, 903 b, or 904 for forming group-III metalnitride layers for the LED/LD structure. In another embodiment, one ormore LED/LD structure layers may be formed in the processing chamber 902after the substrates are cleaned, pretreated, nitriding, and/or coveredwith a buffer layer in the HVPE chamber 902, then moved to processingchambers 903 a, 903 b, or 904 for forming subsequent layers for theLED/LD structure.

During the process of fabricating LED or LD structures, a plurality ofsapphire substrates are first loaded into a processing chamber. Thesapphire substrates are then heated at a temperature ramp-up ratebetween about 1° C./second to about 5° C./second. Ammonia is flow to theprocess chamber at a flow rate between about 3000 sccm to about 9000sccm during temperature ramp-up.

A thermal cleaning is then performed to the sapphire substrates attemperature between 850° C. to about 1100° C. by flowing ammonia andnitrogen carrier gas for about 5 to 15 minutes. The ammonia flow ratemay between about 1 SLM to about 10 SLM.

A pretreatment process is then performed to the sapphire substrateswithin a temperature range between about 625° C. to about 1150° C. byflowing chlorine gas at a flow rate between 200 sccm to about 1000 sccmand ammonia at a flow rate between 500 sccm to about 12,000 sccm.

A GaN film is then formed over the sapphire substrates by a HVPE processat a temperature between about 700° C. to about 1100° C. by flowing agallium containing precursor and ammonia. The gallium containingprecursor is generated by flowing chlorine gas at a flow rate betweenabout 20 sccm to about 150 sccm over solid gallium maintained at atemperature between 550° C. to about 1100° C. Ammonia is flown to theprocessing chamber at a flow rate with in the range between about 3 SLMto about 25 SLM. The GaN has a growth rate between about 0.3 micron/hourto about 150 micron/hour.

Optionally, a nitridation process may be performed prior to one or moreof the previous process steps by flowing ammonia and nitrogen carriergas for about 5 to 15 minutes and heating or maintaining the temperatureof the sapphire substrates at a temperature between 850° C. to about1100° C. The ammonia and nitrogen flow rate may between about 100 sccmto about 500 sccm.

The pressure in the processing chamber during the above cleaning,pretreating, nitridation and deposition may between about 70 Torr toabout 760 Torr.

It should be noted that active gases described above in association withembodiments of the present invention, such as group-III metalprecursors, metal halide gases, halogen gases, ammonia gas, chlorinegas, HCl gas, may be diluted by an inert gas during processing. Suitableinert gas may be argon, helium, nitrogen, or combinations thereof.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1.-12. (canceled)
 13. A method for forming a group-III metal nitridefilm, comprising: heating one or more sapphire substrates to apretreatment temperature; exposing a surface of each of the one or moresapphire substrates to a pretreatment gas mixture when the surface is atthe pretreatment temperature to form a pretreated surface, wherein thepretreatment gas mixture comprises ammonia (NH₃), a group-III metalhalide gas and an etchant containing gas that comprises a halogen gas,wherein exposing the surface of the one or more sapphire substratesfurther comprises forming a region of the pretreated surface thatcomprises aluminum oxynitride or aluminum nitride; and forming a groupIII metal nitride layer over the pretreated surface.
 14. The method ofclaim 13, wherein the halogen gas is chlorine (Cl₂).
 15. The method ofclaim 13, wherein the group-III metal halide gas is formed by exposing ametal source to a first processing gas comprising chlorine (Cl₂), andwherein the metal source comprises aluminum.
 16. The method of claim 13,wherein forming the group-III metal nitride layer further comprisesexposing the one or more sapphire substrates to a nitrogen containingprecursor gas and a gallium chloride containing gas.
 17. The method ofclaim 13, further comprising delivering a nitriding gas mixture thatcomprises ammonia (NH₃) while the temperature of the one or moresapphire substrates is heated to the pretreatment temperature.
 18. Amethod for forming a group-III metal nitride film, comprising: heatingone or more sapphire substrates to a pretreatment temperature; exposinga surface of each of the one or more sapphire substrates to apretreatment gas mixture when the surface is at the pretreatmenttemperature to form a pretreated surface, wherein the pretreatment gasmixture comprises ammonia (NH₃) and an etchant containing gas thatcomprises a halogen gas, wherein exposing the surface of the one or moresapphire substrates further comprises forming a region of the pretreatedsurface that comprises aluminum oxynitride or aluminum nitride; exposinga surface of the one or more sapphire substrates to a nitriding gasmixture for a first period of time; and forming a group Ill metalnitride layer over the pretreated surface.
 19. The method of claim 18,wherein the halogen gas is chlorine (Cl₂).
 20. The method of claim 18,wherein the group-III metal halide gas is formed by exposing a metalsource to a first processing gas comprising chlorine (Cl₂), and whereinthe metal source comprises aluminum.
 21. The method of claim 18, whereinforming the group-III metal nitride layer further comprises exposing theone or more sapphire substrates to a nitrogen containing precursor gasand a gallium chloride containing gas.
 22. The method of claim 18,wherein exposing the surface of the one or more sapphire substrates tothe nitriding gas mixture comprises exposing the pretreated surface tothe nitriding gas mixture.
 23. The method of claim 18, wherein exposingthe surface of the one or more sapphire substrates to the nitriding gasmixture is performed while the temperature of the one or more sapphiresubstrates is heated to the pretreatment temperature.
 24. The method ofclaim 18, wherein forming the group-III metal nitride layer furthercomprises exposing the one or more sapphire substrates to a nitrogencontaining precursor gas, a first group-III metal halide gas and asecond group-III metal halide gas, wherein the first and secondgroup-III metal halide gases each comprise aluminum, gallium or indium.25. The method of claim 24, wherein the nitrogen containing precursorgas comprises ammonia, and the group-III metal halide gas is formed byexposing a metal source to a first processing gas comprising chlorine(Cl₂), and wherein the metal source comprises an element selected fromthe group consisting of gallium, aluminum and indium.
 26. The method ofclaim 18, wherein forming the group-III metal nitride layer furthercomprises: exposing the one or more sapphire substrates to a nitrogencontaining precursor gas and an aluminum chloride containing gas to forman aluminum nitride containing layer on the pretreatment surface; andexposing the formed aluminum nitride containing layer to a nitrogencontaining precursor gas and a gallium chloride containing gas to form agallium nitride containing layer on the aluminum nitride containinglayer.
 27. The method of claim 18, wherein the nitriding gas mixturecomprises ammonia and a carrier gas.
 28. The method of claim 26, whereinthe carrier gas comprises nitrogen.
 29. The method of claim 18, furthercomprising delivering a cleaning gas that comprises ammonia (NH₃) whilethe temperature of the one or more sapphire substrates is heated to thepretreatment temperature.
 30. The method of claim 29, wherein thecleaning gas further comprises nitrogen.
 31. The method of claim 18,wherein the sapphire substrate is a single crystal sapphire substrate.